Since the past, nitrile rubber (acrylonitrile-butadiene copolymer rubber), taking advantage of its oil resistance, mechanical properties, chemical resistance, etc., has been used as a material for hoses, tubes, and other rubber parts for automobiles. Further, hydrogenated nitrile rubber (hydrogenated acrylonitrile-butadiene copolymer rubber) which is obtained by hydrogenating the carbon-carbon double bonds in the polymer main chain of nitrile rubber is further excellent in heat resistance, so is used for seals, belts, hoses, diaphrams, and other rubber parts.
To deal, with this situation, Patent Document 1 proposes a nitrile rubber composition which contains a hydrogenated nitrile rubber having α,β-ethylenically unsaturated dicarboxylic acid mono ester monomer units, a polyamine-based cross-linking agent, and a basic cross-linking accelerator. Using this composition, cross-linked rubber which is excellent in heat resistance, bending fatigue resistance, etc. and is small in compression set is obtained.
On the other hand, in recent years, the market demands on quality have become more sophisticated. In particular, in industrial belts etc., higher load bearing performance is being designed for, so cross-linked rubber with large tensile stress has become sought. However, the cross-linked rubber obtained by cross-linking the nitrile rubber composition which is described in Patent Document 1 is not necessarily sufficient in tensile stress. To deal with the higher demands on load bearing performance in recent years, further improvement in tensile stress has been sought.